DNA sequences which lead to the formation of levans, plasmids containing these sequences as well as a process for preparing transgenic plants

ABSTRACT

There are described DNA sequences, which lead to the formation of polyfructans (levans), plasmids containing theses DNA sequences, as well as a process using these plasmids for preparing transgenic plants with polyfructan (levan) expression.

This application is a division of application Ser. No. 08/381,936 filed on Feb. 9, 1995, now U.S. Pat. No. 5,792,923, which is a 371 of PCT/EP93/02110 filed Aug. 9, 1993.

FIELD OF THE INVENTION

The present invention relates to DNA sequences which lead to the formation of polyfructans (levans), as well as a process for preparing transgenic plants using plasmids on which these DNA sequences are located.

High molecular weight, water soluble, linear polymers, for example those based on polyacrylates or polymethacrylates, are products of mineral oils and have many important uses. In particular their properties in increasing viscosity of aqueous systems, in suspending or sedimentation acceleration and complexing are especially valuable from the technical viewpoint. These products are also used in exceptionally large amounts in super absorbers for water binding and in water dilutable lacquers. In spite of the outstanding positive properties, because such products are difficult to dispose of, their use is increasingly coming under criticism because they are not biodegradable.

Alternatives based on recyclable raw materials, especially starches and cellulose, because of the macromolecular structure of these polysaccharides, have been shown to have limited value. As a replacement for non-biodegradable chemically derived polymers, a number of derivatised high polymeric polysaccharides have been considered. Until now, such polysaccharides could only be obtained biotechnologically via suitable fermentation and transglycosidation processes. The products obtained in this way, such as dextrans and polyfructans (levans) are not competitive as raw materials for mass production.

The present invention relates to DNA sequences which lead to the formation of polyfructans (levans), as well as a process for preparing transgenic plants using plasmids on which these DNA sequences are located.

High molecular weight, water soluble, linear polymers, for example those based on polyacrylates or polymethacrylates, are products of mineral oils and have many important uses. In particular their properties in increasing viscosity of aqueous systems, in suspending or sedimentation acceleration and complexing are especially valuable from the technical viewpoint. These products are also used in exceptionally large amounts in super absorbers for water binding and in water dilutable lacquers. In spite of the outstanding positive properties, because such products are difficult to dispose of, their use is increasingly coming under criticism because they are not biodegradable.

Alternatives based on recyclable raw materials, especially starches and cellulose, because of the macromolecular structure of these polysaccharides, have been shown to have limited value. As a replacement for non-biodegradable chemically derived polymers, a number of derivatised high polymeric polysaccharides have been considered. Until now, such polysaccharides could only be obtained biotechnologically via suitable fermentation and transglycosidation processes. The products obtained in this way, such as dextrans and polyfructans (levans) are not competitive as raw materials for mass production.

Polyfructans are found in a number of monocotyledonous and dicotyledonous higher plants, in green algae as well as in a number of gram positive and gram negative bacteria (Meier and Reid, (1982) Encyclopedia of Plant Physiology, New Series, 13A. 418-471). The role of fructans for the plant development and plant growth is not fully understood. Functions of the fructans that have been proposed are as a protection against freezing at low temperatures, as alternative carbohydrate stores by limiting starch biosynthesis, as well as applied intermediary stores for photoassimilates, situated in the stems of grasses, shortly before their transfer into the seeds.

All fructans contain as starter molecule for the polymerisation reaction, a molecule of sucrose (glucose-fructose) to which fructose polymers are added.

Depending on the coupling of the fructose molecule, fructans of-plant origin can be classified into four classes (Meier and Reid (1982), Encyclopedia of Plant Physiology, New Series, 13A, 418-471):

a) (2-1) coupled β-D-fructans (inulin type)

b) (2-6) coupled β-D-fructans (phlein or levan type)

c) highly branched fructans with a mixture of 2-1and 2-6 couplings.

d) (2-1) coupled β-D-fructans, which in contrast to the types under

a-c, are added completely from fructose residues of polymerisation both from glucose and also from fructose residues from polyfructose residues (neokestose type).

Fructans of bacterial origin correspond either to the levan or to the inulin type (Carlsson (1970) Caries Research 4, 97-113) and Dedonder (1966) Methods Enzymology 8, 500-505).

Experiments on the biosynthesis of fructans in plants and bacteria lead one to conclude that this proceeds by various routes. Bacterial and plant fructans are further distinguished, not particularly in their primary structure but mainly in their molecular weight. Thus, fructans isolated from plants have been shown to have molecular weights of between 5000 and 50,000 d (Pollock and Chatterton (1988) in: The Biochemistry of Plants 14, 109-140), whilst for fructans isolated from bacteria, molecular weights of up to 2,000,000 d have been described (Clarke et al (1991) in: Carbohydrates as Organic Raw Materials, VCH Weinheim, 169-182).

Various microorganisms from the group of Bacillus spp as well as Streptococcus spp produce polyfructoses in which both fructans of the levan type and fructans of the inulin type have been described (Carlsson (1970) Caries Research 4, 97-113 and Dedonder (1966) Methods Enzymology 8, 500-505).

Experiments on biosynthesis pathways have made it clear that, in comparison to biosynthesis pathways in higher plants, there is a more simple pattern and a sharing of only one enzyme. This enzyme with the trivial name levan sucrase is a transfructosylase (sucrose:β-D-fructosyl transferase, E.C.2.4.1.10.), which catalyses the following reaction:

    sucrose+acceptor→glucose+fructosyl acceptor

Representative acceptors are water, alcohol, sugar or polyfructoses. The hypothesis that only one enzyme catalyses this reaction, depends on the one hand on the examination of the protein chemically purified enzyme, and on the other to the fact that the gene for levan sucrase has been isolated from various Bacillus spp. as well as from a Streptococcus spp. and after transfer into E. coli leads to the formation of levan in E. coli (Gay et al (1983) J. Bacteriology 153, 1424-1431 and Sato et al. (1986) Infection and Immunity 52, 166-170).

Until now, genes for levan sucrase from Bacillus amyloliquefaciens (Tang et al. (1990) Gene 96, 89-93) and Bacillus subtilis (Steinmetz et al. (1985) Mol. Gen. Genetics 200, 220-228), have been described, which demonstrate relatively high homology with each other and both of which catalyse the synthesis of fructans of the levan type. Further a fructosyl transferase from Streptococcus mutans (Shiroza et al. (1988) J. Bacteriology 170, 810-816) has been described. This shows little homology to either levan sucrases from Bacillus spp. The fructan formed in Streptococcus mutans is of the inulin type.

In WO 89/12386, there is described the possibility of producing carbohydrate polymers such as dextran or levan in transgenic plants, especially in the fruit of transgenic plants. To prepare these plants, the use of levan sucrases from Aerobacter levanicum, Streptococcus salivarius and Bacillus subtilis and the use of dextran sucrases from Leuconostoc mesenteroides have been described. Further the construction of chimeric genes is described which may be suitable for the expression of the levan sucrase from Bacillus subtilis as well as the dextran sucrase from Leuconostoc mesenteroides in transgenic plants. Also described is the preparation of transgenic plants containing these constructs. Further, the preparation of transgenic plants that contain these constructs are described. Whether polyfructans can actually be produced by the described process is not known. There is also described a series of processes for modifying the carbohydrate concentration and/or concentrating carbohydrate in transgenic plants by means of biotechnological methods. Thus, in view of the fact that increasing starch concentration and modification of the starch in physical and chemical respects is already known, then a modification of the carbohydrate content of potato plants by raising or lowering the ADP-glucose-pyrophosphorylase activity can be achieved (EP 455 316).

From EP 442 592 it is further known that a modification of the distribution of photoassimilates by means of cytosolic and apoplastic invertase is possible and that the yield as well as the drought and frost resistance of potato plants through expression of a heterologous pyrophosphatase gene in potato plants can be modified.

In order to adapt the physico-chemical parameters of raw materials which are increasingly being used, such as polysaccharides, to the requirements of the chemical industry, as well as to minimise the costs of obtaining these products, processes for the preparation of trans-genic plants have to be developed which lead in comparison with known processes to better, higher yielding plants.

SUMMARY OF THE INVENTION

It has now been surprisingly found that the DNA sequence of the levan sucrase from a gram-negative bacterium of the species Erwinia amylovora with the nucleotide sequence (Seq - ID NO 1): makes possible the preparation of large amounts of polyfructans (levans) in transgenic plants, which decisively meet the needs of the chemical industry in respect of recyclable raw materials.

By integration of a DNA sequence in a plant genome, on which the above given DNA sequence is located, the polyfructan (levan), expression in plants, especially in leaves and tubers is made possible. The levan sucrase of the invention shows, at the DNA level, no significant homology to the known levan sucrases.

The invention further provides a process for the preparation of transgenic plants with polyfructan (levan) expression in leaves and tubers that comprises the following steps:

(a) preparation of a DNA sequence with the following partial sequences:

i) a promoter which is active in plants and ensures formation of an RNA in the intended target tissues or target cells,

ii) a DNA sequence of a levan sucrase, and

iii) a 3'-non-translated sequence, which in plant cells leads to the termination of the transcription as well as the addition of poly A residues to the 3'-end of the RNA,

(b) transfer and integration of the DNA sequence in the plant genome of a recombinant double stranded DNA molecule from plant cells using a plasmid, and

(c) regeneration of intact whole plants from the transformed plant cells.

The levan sucrose obtained in process step (a,) ii) preferably shows the nucleotide sequence noted under sequence IC No 1.

The levan sucrase catalyses the following reaction:

    Sucrose-(fructose).sub.n +sucrose→sucrose+(fructose).sub.n+l+ glucose.

Using this process in principle, all plants can be modified in respect to a polyfructan (levan) expression, preferably crops such as maize, rice, wheat, barley, sugar beet, sugar cane, tobacco and potatoes.

In process step (b), in principle all plasmids can be used which have the DNA sequence given under sequence ID No 1. Preferably used are plasmid p35s-CW-LEV (DS3.M) 7186), plasmid P35s-CY-LEV (DSM 7187) or plasmid P33-CW-LEV (DSM 7188).

Since sucrose represents the substrate for the levan sucrase, the production of polyfructans is especially advantageous in those organs which store large amounts of sucrose. Such organs are for example the roots of sugar beet or the stems of sugar cane. It is especially useful in genetically modified potatoes, which store sucrose in their tubers, through blocking of starch biosynthesis

Biosynthesis of sucrose takes place in the cytosol, whilst in contrast, storage is in the vacuole. During transport into the storage tissues of sugar beet or potato or into the endosperm of seeds, the sucrose must cross the intercellular space. In production of polyfructans, all three cell compartments are suitable, i.e. cytosol, vacuole and intercellular space.

The coding sequence of the levan sucrose of the nucleotide sequence ID No 1 can be provided with a promoter that ensures the transcription in specified orders which is coupled in sense orientation (3'-end of the promoter to the 5'-end of the coding sequence) on the coding sequence which codes the enzyme to be formed. The termination signal which determines the termination of the mRNA synthesis is adhered to the 3'-end of the coding sequence. In order to direct the enzyme which is expressed in specified sub-cellular compartments such as chloroplasts, amyloplasts, mitochondria, vacuoles, cytosol or intercellular space, a so-called signal sequence or a transit peptide coding sequence can be positioned between the promoter and the coding sequence. This sequence must be in the same reading frame as the coding sequence of the enzyme.

For the introduction of the DNA sequence of the invention in higher plants, a large number of cloning vectors are available, which contain a replication signal for E. coli and a marker, which allows a selection of the transformed cells. Examples of vectors are pBR 322, pUC-series, M13 mp-series, pACYC 184; EMBL 3 etc. According to the introduction method of the desired gene in the plant, other DNA sequences may be suitable. Should the Ti-or Ri-plasmid.be used, e.g. for the transformation of the plant cell, then at least the right boundary, often however both the right and left boundary of the Ti-and Ri-Plasmid T-DNA, is attached, as a flanking region, to the gene being introduced. The use of T-DNA for the transformation of plants cells has been intensively researched and is well described in EP 120 516; Hoekama, In: The Binary Plant Vector System, Offset-drukkerij Kanters B.V. Alblasserdam, (1985), Chapter V; Fraley, et al., Crit. Rev. Plant Sci., 4:1-46 and An et al. (1985) EMBO J. 4:277-287. Once the introduced DNA is integrated in the genome, it is as a rule stable there and remains also in the offspring of the original transformed cells. It normally contains a selection marker, which induces resistance in the transformed plant cells against a biocide or antibiotic such as kanamycin, G 418, bleomycin, hygromycin or phosphinotricin etc. The individual marker employed should therefore allow the selection of transformed cells from cells, which lack the introduced DNA.

For the introduction of DNA into a plant, besides transformation using Agrobacteria, there are many other techniques available. These techniques include the fusion of protoplasts, microinjection of DNA and electroporation, as well as ballistic methods and virus infection.

From the transformed plant material, whole plants can be regenerated in a suitable medium, which contains antibiotics or biocides for the selection. The resulting plants can then be tested for the presence of introduced DNA. No special demands are placed on the plasmids in injection and electroporation. Simple plasmids, such as e.g. pUC-derivatives can be used. Should however whole plants be regenerated from such transformed cells the presence of a selectable marker gene is necessary. The transformed cells grow within the plants in the usual manner (see also McCormick et al.(1986) Plant Cell Reports 5:81-84). These plants can be grown normally and crossed with plants, that possess the same transformed genes or different. The resulting hybrid individuals have the corresponding phenotypical properties.

Deposits

The following plasmids were deposited at the Deutschen Sammlung von Mikroorganismen (DSM) in Braunschweig, Germany on the 16.07.1992 (deposit number):

Plasmid p35s-CW-LEV (DSM 7186)

Plasmid p35s-CY-LEV (DSM 7187)

Plasmid p33-CW-LEV (DSM 7188)

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the structure of the p35-CW-LEV plasmid. It comprises the three fragments A, B and C. Fragment A contains the 35s promoter of the cauliflower mosaic virus (CaMV), nucleotides 6906-7437. Fragment B contains the sequence of the nucleotides 689-2122 of the levan sucrase from Erwinia amylovora (Seq. ID No.1). Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5, nucleotides 11749-11939.

FIG. 2 shows the structure of the p35s-CY-LEV plasmid. It comprises the three fragments A, B and C. Fragment A contains the 35s promoter of the cauliflower mosaic virus (CaMV), nucleotides 6909-7437.Fragment B contains the sequence of the nucleotides 864-2122 of the levan sucrase from Erwinia amylovora (Seq. ID No.1). Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5.

FIG. 3 shows the structure of the p33-CW-LEV plasmid. It comprises the three fragments A, B and C. Fragment A contains the Dral-DraI-fragment (position -1512 to position +14) of the promoter region of the patatin gene B33. Fragment B contains the sequence of the nucleotides 689-2122 of the levan sucrase from Erwinia amylovora (Sea. ID No.1). Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5, nucleotides 11749-11939.

FIG. 4 shows the detection of polyfructan in transformed tobacco plants (No. 2, 3 and 13). In this: Fru=fructose, Suc=sucrose, Kes=kestose c1=control 1, c2=control 2, M=marker

FIG. 5 shows NMR peaks for levan extracted from transformed plants.

DETAILED DESCRIPTION OF THE INVENTION

In order to understand the examples forming the basis of this

invention all the processes necessary for these tests and which are known per se will first of all be listed:

1. Cloning process

The vector pUC 18 (Yanisch-Perron et al. (1985) Gene 33:103-119) was used for cloning.

For the plant transformations, the gene constructs were cloned in the binary vector BIN 19 (Bevan (1984) Nucl. Acids Res 12: 8711-8720)

2. Bacterial strains

The E. coil strain BMH71-18 (Messing et al., Proc. Natl. Acad. Sci. U.S.A. (1977), 24, 6342-6346) or TB1 was used for the pUC vectors. TB1 is a recombinant-negative, tetracycline-resistant derivative of strain JM101 (Yanisch-Perron et al., Gene (1985), 33, 103-119). The genotype of the TB1 strain is (Bart Barrel, personal communication): F' (traD36, proAB, lacI, lacZ.increment.M15), .increment.(lac, pro), SupE, thiS, recA, Sr1::Tn10(TcR).

The transformation of the plasmids into the potato plants was carried out using Agrobacterium tumefaciens strain LBA4404 (Bevan, (1984), Nuci. Acids Res. 12, 8711-8720).

3. Transformation of Agrobacterium tumefaciens

In the case of BIN19 derivatives, the insertion of the DNA into the Agrobacterium effected by direct transformation in accordance with the method of Holsters et al., (1978) (Mol Gene Genet 163:181-187). The plasmid DNA of the transformed Agrobacterium was isolated in accordance with the method of Birnboim and Doly (1979) (Nucl Acids Res 7:1513-1523) and was analysed by gel electrophoresis after suitable restriction cleavage.

4. Plant transformation

A) Tobacco: 10 ml of an overnight culture of Agrobacterium tumefaciens, grown under selection, were centrifuged off, the supernatant was discarded, and the bacteria were resuspended in the same volume of antibiotic-free medium. In a sterile petri dish, leaf discs of sterile plants (approximately 1 cm²), the central vein of which had been removed, were immersed in this bacterial suspension. The leaf discs were then placed in a closely packed arrangement in petri dishes containing MS medium (Murashige et al. (1962) Physiologia Plantarum 15, 473-497) with 2% sucrose and 0.8% bacto agar. After two days incubation in the dark at 25° C., they were transferred onto MS medium containing 100 mg/l kanamycin, 500 mg/l claforan, 1 mg/l benzylaminopurine (BAP), 0.2 mg/l of naphthylacetic acid (NAA) and 0.8 % bacto agar. Growing shoots were transferred onto hormone-free MS medium with 250 mg/l of claforan.

B) Potato: Ten small leaves, wounded with a scalpel, of a sterile potato culture were placed in 10 ml of MS medium with 2% sucrose containing 30-50 μl of an Agrobacterium tumefaciens overnight culture grown under selection. After 3-5 minutes gentle shaking, the leaves were laid out on MS medium of 1.6% glucose, 2 mg/l of zeatin ribose, 0.02 mg/l of naphthylacetic acid, 0.02 mg/l of gibberellic acid, 500 mg/l of claforan, 50 mg/l of kanamycin and 0.8% bacto agar. After incubation for one week at 25° C. and 3000 lux, the claforan concentration in the medium was reduced by half. Further cultivation was carried out using the method described by Rocha-Sosa et al. (1989) EMBO Journal 8, 29).

5. Analysis of genomic DNA from transgenic plants

The isolation of genomic plant DNA was carried out according to Rogers et al. (1985) Plant Mol Biol 5, 69-76).

For the DNA analysis, after suitable restriction cleavage, 10 to 20 μg of DNA were analysed, by means of Southern blotting, for the integration of the DNA sequences to be investigated.

6. Analysis of the total RNA from transqenic plants

The isolation of plant total RNA was carried out according to Logemann et al. (1987), Analytical Biochem. 163, 16-20.

For the analysis, 50 μg portions of total RNA were investigated, by means of Northern blotting, for the presence of the transcripts sought.

7. Extraction and determination of polyfructose in plants

The extraction and determination were carried out according to the method of Portis H. G. (1990), Meth. Plant Biochem. 2, 353-369.

Example 1

Preparation of plasmid p35s-CW-LEV and insertion of the plasmid into the genome of tobacco and potato

The plasmid p35s-CW-LEV comprises the three fragments A, B and C, which were cloned in the cutting sites for restriction enzymes of the polylinker from pUC 18 (see FIG. 1).

Fragment A contains the 35S promoter of cauliflower mosaic virus (CaMV). It contains a fragment that includes the nucleotides 6909 to 7437 of CaMV (Franck et al. (1980) Cell 21, 285-294) and was isolated as Eco RI-Kpn I fragment from plasmid pDH 51 (Pietrzak et al., Nucleic Acids Research 14, 5857-5868) and cloned between the Eco RI-Kpn I cutting sites of the polylinker of plasmid pUC 18.

Fragment B contains the sequence of the nucleotides 689-2122 of the gene of the levan sucrase from Erwinia amylovora (Seq. ID No.1) and was cloned between the BamHI/SalI cutting positions of the polylinker of PUC 18.

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5 (Gielen et al (1984); EMBO J. 3, 835-846) nucleotides 11749-11939 which was insolated as Pvu II-Hind III fragment from the plasmid pAGV 40 (Herrera-Estrella et al (1983) Nature 303, 209-213) and, after addition of Sph I linkers to the Pvu II cutting positions, was cloned between the SphI-Hind III cutting positions of the polylinker of pUC 18.von pUC 18. The plasmid p35s-CW-LEV has a size of 2151 bp.

The part of the plasmid p35s-CW-LEV comprising the fragments A, B and C was introduced in binary vectors and using the Agrobacterium system was introduced into tobacco and potato plants. Intact plants were regenerated from transformed cells. The analysis of the leaves from a series of Tobacco plants transformed with this gene, clearly showed the presence of polyfructan (levan) which is traced back to the expression of the gene 35s-Cw-LEV (see FIG. 4).

Example 2

Preparation of plasmid p35s-CY-LEV and insertion of the plasmid into the genome of tobacco and potato

This Example was carried out in an analogous manner to that described under Example 1, but with the modification, that the Fragment B (coding for the levan sucrase) is shortened on the nucleotide at the 5'-end. This results in the expression of the protein in the cytosol of transgenic plants.

The plasmid p35s-CY-LEV comprises the three fragments A, B and C, which were cloned in the cutting sites for restriction enzymes of the polylinker from pUC 18 (see FIG. 2). Fragment A contains the 35S promoter of cauliflower mosaic virus (CaMV). It contains a fragment that includes the nucleotides 6909 to 7437 of CaMV (Franck et al. (1980) Cell 21, 285-294) and was isolated as Eco RI-Kpn I fragment from plasmid pDH 51 (Pietrzak et al., Nucleic Acids Research 14, 5857-5868) and cloned between the-Eco RI-Kpn I cutting sites of the polylinker of plasmid pUc 18. Fragment B contains the sequence of the nucleotides 864-2122 of the gene of the levan sucrase from Erwinia amylovora (Seq. ID No.1) and was cloned between the SmaI/SalI cutting positions of the polylinker of pUC 18. Fragment C contains the polyadenylation signal of the gene 3 of the T- DNA of the Ti-plasmid, pTi ACH 5 (Gielen et al (1984); EMBO J. 3, 835-846) nucleotides 11749-11939 which was insolated as Pvu II-Hind III fragment from the plasmid pAGV 40 (Herrera-Estrella et al (1983) Nature 303, 209-213) and, after addition of Sph I linkers to the Pvu II cutting positions, was cloned between the SphI-Hind III cutting positions of the polylinker of pUC 18.von pUC 18. The plasmid p35s-CY-LEV has a size of 1976 bp.

The part of the plasmid p35s-CY-LEV comprising the fragments A, B and C was introduced in binary vectors and using the Agrobacterium system was introduced into tobacco and potato plants. Intact plants were regenerated from transformed cells.

Example 3

Preparation of plasmid p35s-CY-LEV and insertion of the plasmid into the genome of tobacco and potato

This Example was carried out in an analogous manner to that described under Example 1, but with the 35s promoter being replaced with the promoter of the class I patatin Gene B33 (Rocha-Sosa et al, (1989) EMBO J 8, 23-29) The plasmid p33-CW-LEV comprises the three fragments A, B and C, which were cloned in the cutting sites for restriction enzymes of the poglylinker from pUC 18 (see FIG. 3). Fragment A contains the Dral-Dral fragment (position -1512 to position +14) of the promoter region of the patatin gene B33 (Rocha-Sosa et al (1989) EMBO J. 8, 23-29), which was cloned in the Sma I position of the polylinker of pUC 118. Fragment B contains the sequence of the nucleotides 689-2122 of the gene of the levan sucrase from Erwinia amylovora (Seq. ID No.1) and was cloned between the BamHI/SalI cutting positions of the polylinker of pUC 18.

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5 (Gielen et al (1984); EMBO J. 3, 835-846) nucleotides 11749-11939 which was insolated as Pvu II-Hind III fragment from the plasmid pAGV 40 (Herrera-Estrella et al (1983) Nature 303, 209-213) and, after addition of Sph I linkers to the Pvu II cutting positions, was cloned between the SphI-Hind III cutting positions of the polylinker of pUC 18.von pUC 18. The plasmid p33-CW-LEV has a size of 3149 bp.

The part of the plasmid p33-CW-LEV comprising the fragments A, B and C was introduced in binary vectors and using the Agrobacterium system was introduced into tobacco and potato plants. Intact plants were regenerated from transformed cells. The analysis of the leaves from a series of Tobacco plants transformed with this gene, clearly showed the presence of polyfructan (levan) which is traced back to the expression of the gene 33-CW-LEV.

Example 4

Analysis of μ2,6-D-Fructofurane (levan) synthesized in transgenic plants by 13C-NMR spectroscopy

The analysis of transgenic plants transformed with the construct p35S-CW-LEV is shown as an example. This analysis can equally be applied to transgenic plants transformed with the constructs p35S-CW-LEV or p35S-CY-LEV.

To obtain sufficient amounts of levan synthesised by transgenic plants to perform NMR spectroscopy, about 10 g of leaf tissue was ground in 10 ml of water. The homogenate is then centrifuged at 4000 Rpm in a Beckman Minifuge and the supernatant is applied to a PD 10 column (LKB-Pharmacia) to remove lower molecular weight compounds. The column had been equilibrated with water before the 2.5 ml of the supernatant are applied and higher molecular weight compounds were then eluted with 3.5 ml of water. The eluate was further purified by adding ion exchange beads (AG 501 X8, Biorad) and shaking for 30 minutes. After centrifugation at 4000 Rpm (Minifuge, Beckman) to remove the beads, the supernatant is applied to a Sepharose 4B column (diameter 16 cm, separating volume 24 ml) to remove the short sugar chains. The eluate is vacuum dried in a vacuum centrifuge (univapo 150 H. Uniquip, Martinsried (FRG)) and then analysed by 13C-NMR under the following conditions:

    ______________________________________                                         PULPROG zgdc30       F2-Processing                                                                                                           parameters                                        SOLVENT    D20               SI                                                    32768                                       AQ         1.3762726 sec     SF               100.5485322 MHz                  FIDRES     0.363305 Hz       WDW              EM                               DW         21.0 usec         SSB              0                                RG         32768             LB               0.50 Hz                          NUCLEUS    13 C              GB               0                                D11        0.0300000 sec     PC               1.40                             P31        100.0 usec                                                          S2         20 dB              10 NMR plot                                                                    parameters                                       HLT        1 dB               CX               33.00 cm                        D1         1.0000000 sec      FTP              123.000 ppm                     P1         6.5 usec           FT               12367.47 Hz                     DE         26.3 usec          F2P              -6.000 ppm                      SF01       100.5597430 MHz    F2               -603.29 Hz                      SWH        23809.58 Hz        PPMCM            3.90909 ppm/cm                  TD         65536              HZCM             393.05334 Hz/cm                 NS         8000                                                                DS         2                                                                 ______________________________________                                    

The result of the analysis is shown in FIG. 5. The pattern of NMR peaks obtained is the same as it is obtained for levan as published by Gross et al., 1992, Physiol Mol Plant Pathol 40:371.

This proves that the transformed plants synthesise levan after transformation by one of the constructs described in examples 1 to 3.

    __________________________________________________________________________     #             SEQUENCE LISTING                                                    - -  - - (1) GENERAL INFORMATION:                                              - -    (iii) NUMBER OF SEQUENCES: 2                                            - -  - - (2) INFORMATION FOR SEQ ID NO:1:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1438 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: DNA (genomic)                                      - -    (iii) HYPOTHETICAL: NO                                                  - -     (iv) ANTI-SENSE: NO                                                    - -     (vi) ORIGINAL SOURCE:                                                           (A) ORGANISM: Erwinia a - #mylovora                                            (C) INDIVIDUAL ISOLATE: - #Strain Ea/74m                                       (G) CELL TYPE: bacteriu - #m                                          - -    (vii) IMMEDIATE SOURCE:                                                          (A) LIBRARY: genomic                                                           (B) CLONE: DH5alpha pEA - #-LS5                                       - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 155..1399                                                        (D) OTHER INFORMATION: - #/note= "Levansucrase"                       - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                - - GGATCCCCCG GGCTGCAGCG ATCATGGTTA TTTATAAGGG ATTGTTATGT CC -             #TGAAAACC     60                                                                  - - ACACAACAGA ACCAGAGTGA TTTCAAAAAA TAAAAAGCTA TTAATATACA GA -             #CCTTCAGC    120                                                                  - - AAGAAGGTAT TCGAAATAAC CTGTGAGGAT ATTT ATG TCA GAT T - #AT AAT TAT             172                                                                                         - #                  - #  Met Ser Asp Tyr Asn Tyr                              - #                  - #    1              - # 5              - - AAA CCA ACG CTG TGG ACT CGT GCC GAT GCA TT - #G AAA GTT CAT GAG GAT           220                                                                        Lys Pro Thr Leu Trp Thr Arg Ala Asp Ala Le - #u Lys Val His Glu Asp                         10     - #             15     - #             20                   - - GAC CCA ACC ACA ACT CAA CCG GTT ATT GAC AT - #T GCA TTC CCG GTA ATG           268                                                                        Asp Pro Thr Thr Thr Gln Pro Val Ile Asp Il - #e Ala Phe Pro Val Met                     25         - #         30         - #         35                       - - AGT GAA GAA GTC TTT ATT TGG GAT ACC ATG CC - #A TTG CGA GAC TTC GAC           316                                                                        Ser Glu Glu Val Phe Ile Trp Asp Thr Met Pr - #o Leu Arg Asp Phe Asp                 40             - #     45             - #     50                           - - GGA GAG ATT ATC TCT GTA AAT GGT TGG TGT AT - #T ATT TTT ACG CTA ACA           364                                                                        Gly Glu Ile Ile Ser Val Asn Gly Trp Cys Il - #e Ile Phe Thr Leu Thr             55                 - # 60                 - # 65                 - # 70        - - GCA GAT CGC AAC ACT GAT AAT CCG CAA TTC CA - #G GAT GAA AAT GGC AAT           412                                                                        Ala Asp Arg Asn Thr Asp Asn Pro Gln Phe Gl - #n Asp Glu Asn Gly Asn                             75 - #                 80 - #                 85               - - TAT GAT ATT ACT CGT GAC TGG GAA GAC AGA CA - #T GGT CGT GCG CGT ATT           460                                                                        Tyr Asp Ile Thr Arg Asp Trp Glu Asp Arg Hi - #s Gly Arg Ala Arg Ile                         90     - #             95     - #            100                   - - TGT TAT TGG TAC TCA CGC ACC GGT AAA GAC TG - #G ATT TTT GGC GGT CGG           508                                                                        Cys Tyr Trp Tyr Ser Arg Thr Gly Lys Asp Tr - #p Ile Phe Gly Gly Arg                    105          - #       110          - #       115                       - - GTA ATG GCC GAA GGT GTC GCA CCG ACG ACG CG - #T GAG TGG GCC GGA ACC           556                                                                        Val Met Ala Glu Gly Val Ala Pro Thr Thr Ar - #g Glu Trp Ala Gly Thr                120              - #   125              - #   130                           - - CCG ATC CTT TTA AAC GAT CGG GGC GAT ATT GA - #C CTG TAT TAT ACC TGT           604                                                                        Pro Ile Leu Leu Asn Asp Arg Gly Asp Ile As - #p Leu Tyr Tyr Thr Cys            135                 1 - #40                 1 - #45                 1 -       #50                                                                               - - GTC ACT CCG GGT GCA ACC ATT GCC AAA GTG CG - #C GGT AAA ATC GTC         ACT      652                                                                     Val Thr Pro Gly Ala Thr Ile Ala Lys Val Ar - #g Gly Lys Ile Val Thr                           155  - #               160  - #               165               - - TCC GAT CAA AGT GTA AGC CTG GAA GGT TTT CA - #G CAG GTT ACA TCA CTT           700                                                                        Ser Asp Gln Ser Val Ser Leu Glu Gly Phe Gl - #n Gln Val Thr Ser Leu                        170      - #           175      - #           180                   - - TTC TCT GCT GAC GGG ACT ATT TAC CAG ACG GA - #A GAG CAG AAC GCT TTC           748                                                                        Phe Ser Ala Asp Gly Thr Ile Tyr Gln Thr Gl - #u Glu Gln Asn Ala Phe                    185          - #       190          - #       195                       - - TGG AAC TTC CGT GAC CCA AGC CCA TTC ATT GA - #C AGG AAT GAT GGC AAA           796                                                                        Trp Asn Phe Arg Asp Pro Ser Pro Phe Ile As - #p Arg Asn Asp Gly Lys                200              - #   205              - #   210                           - - TTA TAT ATG CTG TTT GAA GGA AAC GTG GCG GG - #G CCG CGC GGT TCG CAC           844                                                                        Leu Tyr Met Leu Phe Glu Gly Asn Val Ala Gl - #y Pro Arg Gly Ser His            215                 2 - #20                 2 - #25                 2 -       #30                                                                               - - GAA ATT ACC CAG GCT GAG ATG GGT AAT GTG CC - #G CCG GGT TAT GAA         GAT      892                                                                     Glu Ile Thr Gln Ala Glu Met Gly Asn Val Pr - #o Pro Gly Tyr Glu Asp                           235  - #               240  - #               245               - - GTG GGT GGC GCA AAA TAT CAG GCA GGC TGT GT - #T GGT CTG GCT GTG GCC           940                                                                        Val Gly Gly Ala Lys Tyr Gln Ala Gly Cys Va - #l Gly Leu Ala Val Ala                        250      - #           255      - #           260                   - - AAA GAC CTG TCA GGC AGT GAG TGG CAA ATC CT - #G CCT CCG CTG ATC ACC           988                                                                        Lys Asp Leu Ser Gly Ser Glu Trp Gln Ile Le - #u Pro Pro Leu Ile Thr                    265          - #       270          - #       275                       - - GCT GTT GGC GTA AAC GAT CAG ACT GAA CGC CC - #T CAT TTT GTC TTC CAG          1036                                                                        Ala Val Gly Val Asn Asp Gln Thr Glu Arg Pr - #o His Phe Val Phe Gln                280              - #   285              - #   290                           - - GAT GGT AAA TAC TAT CTG TTC ACC ATT AGC CA - #T AAG TAC ACT TTT GCC          1084                                                                        Asp Gly Lys Tyr Tyr Leu Phe Thr Ile Ser Hi - #s Lys Tyr Thr Phe Ala            295                 3 - #00                 3 - #05                 3 -       #10                                                                               - - GAT AAC CTG ACC GGC CCT GAT GGA GTG TAT GG - #C TTT GTA AGC GAT         AAA     1132                                                                     Asp Asn Leu Thr Gly Pro Asp Gly Val Tyr Gl - #y Phe Val Ser Asp Lys                           315  - #               320  - #               325               - - CTT ACC GGC CCT TAC ACG CCG ATG AAT AGC TC - #C GGG CTG GTG CTG GGC          1180                                                                        Leu Thr Gly Pro Tyr Thr Pro Met Asn Ser Se - #r Gly Leu Val Leu Gly                        330      - #           335      - #           340                   - - AAC CCG TCT TCA CAA CCT TTC CAG ACA TAT TC - #A CAC TAT GTT ATG CCT          1228                                                                        Asn Pro Ser Ser Gln Pro Phe Gln Thr Tyr Se - #r His Tyr Val Met Pro                    345          - #       350          - #       355                       - - AAT GGG CTG GTC ACT TCC TTT ATT GAC AGT GT - #T CCG TGG AAA GGT AAG          1276                                                                        Asn Gly Leu Val Thr Ser Phe Ile Asp Ser Va - #l Pro Trp Lys Gly Lys                360              - #   365              - #   370                           - - GAC TAT CGC ATT GGC GGT ACT GAA GCT CCG AC - #C GTA AAA ATT CTG TTG          1324                                                                        Asp Tyr Arg Ile Gly Gly Thr Glu Ala Pro Th - #r Val Lys Ile Leu Leu            375                 3 - #80                 3 - #85                 3 -       #90                                                                               - - AAA GGC GAT CGC TCA TTT ATT GTT GAT AGC TT - #C GAT TAT GGA TAT         ATT     1372                                                                     Lys Gly Asp Arg Ser Phe Ile Val Asp Ser Ph - #e Asp Tyr Gly Tyr Ile                           395  - #               400  - #               405               - - CCG GCA ATG AAA GAC ATT ACT TTA AAA TAAGTCTGT - #T GTCGATATCA                1419                                                                        Pro Ala Met Lys Asp Ile Thr Leu Lys                                                        410      - #           415                                          - - AGCTTATCGA TACCGTCGA             - #                  - #                      143 - #8                                                                   - -  - - (2) INFORMATION FOR SEQ ID NO:2:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 415 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                - - Met Ser Asp Tyr Asn Tyr Lys Pro Thr Leu Tr - #p Thr Arg Ala Asp Ala         1               5 - #                 10 - #                 15               - - Leu Lys Val His Glu Asp Asp Pro Thr Thr Th - #r Gln Pro Val Ile Asp                    20     - #             25     - #             30                   - - Ile Ala Phe Pro Val Met Ser Glu Glu Val Ph - #e Ile Trp Asp Thr Met                35         - #         40         - #         45                       - - Pro Leu Arg Asp Phe Asp Gly Glu Ile Ile Se - #r Val Asn Gly Trp Cys            50             - #     55             - #     60                           - - Ile Ile Phe Thr Leu Thr Ala Asp Arg Asn Th - #r Asp Asn Pro Gln Phe        65                 - # 70                 - # 75                 - # 80        - - Gln Asp Glu Asn Gly Asn Tyr Asp Ile Thr Ar - #g Asp Trp Glu Asp Arg                        85 - #                 90 - #                 95               - - His Gly Arg Ala Arg Ile Cys Tyr Trp Tyr Se - #r Arg Thr Gly Lys Asp                   100      - #           105      - #           110                   - - Trp Ile Phe Gly Gly Arg Val Met Ala Glu Gl - #y Val Ala Pro Thr Thr               115          - #       120          - #       125                       - - Arg Glu Trp Ala Gly Thr Pro Ile Leu Leu As - #n Asp Arg Gly Asp Ile           130              - #   135              - #   140                           - - Asp Leu Tyr Tyr Thr Cys Val Thr Pro Gly Al - #a Thr Ile Ala Lys Val       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Arg Gly Lys Ile Val Thr Ser Asp Gln Ser Va - #l Ser Leu Glu Gly         Phe                                                                                              165  - #               170  - #               175              - - Gln Gln Val Thr Ser Leu Phe Ser Ala Asp Gl - #y Thr Ile Tyr Gln Thr                   180      - #           185      - #           190                   - - Glu Glu Gln Asn Ala Phe Trp Asn Phe Arg As - #p Pro Ser Pro Phe Ile               195          - #       200          - #       205                       - - Asp Arg Asn Asp Gly Lys Leu Tyr Met Leu Ph - #e Glu Gly Asn Val Ala           210              - #   215              - #   220                           - - Gly Pro Arg Gly Ser His Glu Ile Thr Gln Al - #a Glu Met Gly Asn Val       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Pro Pro Gly Tyr Glu Asp Val Gly Gly Ala Ly - #s Tyr Gln Ala Gly         Cys                                                                                              245  - #               250  - #               255              - - Val Gly Leu Ala Val Ala Lys Asp Leu Ser Gl - #y Ser Glu Trp Gln Ile                   260      - #           265      - #           270                   - - Leu Pro Pro Leu Ile Thr Ala Val Gly Val As - #n Asp Gln Thr Glu Arg               275          - #       280          - #       285                       - - Pro His Phe Val Phe Gln Asp Gly Lys Tyr Ty - #r Leu Phe Thr Ile Ser           290              - #   295              - #   300                           - - His Lys Tyr Thr Phe Ala Asp Asn Leu Thr Gl - #y Pro Asp Gly Val Tyr       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Gly Phe Val Ser Asp Lys Leu Thr Gly Pro Ty - #r Thr Pro Met Asn         Ser                                                                                              325  - #               330  - #               335              - - Ser Gly Leu Val Leu Gly Asn Pro Ser Ser Gl - #n Pro Phe Gln Thr Tyr                   340      - #           345      - #           350                   - - Ser His Tyr Val Met Pro Asn Gly Leu Val Th - #r Ser Phe Ile Asp Ser               355          - #       360          - #       365                       - - Val Pro Trp Lys Gly Lys Asp Tyr Arg Ile Gl - #y Gly Thr Glu Ala Pro           370              - #   375              - #   380                           - - Thr Val Lys Ile Leu Leu Lys Gly Asp Arg Se - #r Phe Ile Val Asp Ser       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Phe Asp Tyr Gly Tyr Ile Pro Ala Met Lys As - #p Ile Thr Leu Lys                          405  - #               410  - #               415             __________________________________________________________________________ 

We claim:
 1. An isolated DNA molecule encoding a polyfructan sucrase comprising the sequence set forth in SEQ ID NO.
 1. 2. A plasmid containing a DNA molecule according to claim
 1. 3. Plasmid p35s-CW-LEV (DSM 7186).
 4. Plasmid p35s-CY-LEV (DSM 7187).
 5. Plasmid p33-CW-LEV (DSM 7188).
 6. Process for the preparation of transgenic plants with polyfructan expression in leaves or tubers which comprises the following steps:(a) preparation of a DNA molecule with the following partial sequences:i) a promoter which is active in plants and ensures formation of an RNA in the intended target tissues or target cells, ii) DNA molecule of a levan sucrase according to claim 1, and iii) a 3'-non-translated sequence, which in plant cells leads to the termination of the transcription as well as the addition of poly A residues to the 3'-end of the RNA, (b) transfer and integration of said DNA molecule in the plant genome, and (c) regeneration of intact whole plants from the transformed plant cells.
 7. Process according to claim 6, wherein the polyfructan sucrase expression in leaves and tubers leads to a polyfructan sucrase activity in the chloroplasts, amyloplasts, mitochondria, cytosol, or vacuoles.
 8. A plant obtained by the process according to any one of claims 6 or
 7. 9. A plant according to claim 8, which is crop plant.
 10. A plant according to claim 8, which is a maize, rice, wheat, barley, sugar beet, sugar cane, tobacco or potato plant.
 11. A method for the preparation of plants with polyfructan expression in leaves and tubers comprising transforming a plant cell so as to contain and express the DNA of claim 1, and growing the plant from the cell.
 12. A method for the preparation of plants with polyfructan expression in leaves and tubers comprising transforming a plant cell so as to contain a plasmid according to any one of claims 2, 3, 4 or 5 and express the DNA therein, and growing the plant from the cell. 